Fuel dispensers such as jerry cans have been used for many years as a convenient and safe way to transport fluids, especially fuel. There are many designs now available including cans with and without spouts, cans made of metal and others made of plastic. Jerry cans and other designs of fuel container are commonly used to transport petrol, diesel or gasoline.
One common type of internal combustion engine is the reciprocating two stroke engine. Many small petrol driven, hand-held devices such as chainsaws and hedge trimmers and outboard engines for boats use two stroke engines.
Unlike a typical four stroke engine, these and certain other engines cannot be lubricated using oil stored in the crankcase and sump, because the crankcase is used to pump a fuel/air mix into the cylinder. The moving parts of two-stroke and other similar engines are therefore commonly lubricated by oil that has been added to the fuel. The moving parts include the crankshaft and piston. The fuel and oil can be mixed in the fuel tank or premixed to improve the homogeneity of the mixture. The ratio of fuel to oil required depends on the type of engine. A chainsaw engine is unlikely to require the same ratio of fuel to oil as, for example a hedge trimmer. It is possible to use the incorrect fuel to oil mix and it is at least inconvenient to check and mix oil into the fuel at the correct concentration/ratio.
Traditionally oil is added to the fuel tank before filling the tank with fuel (petrol in most cases). The subsequent addition of fuel helps to mix the oil and fuel, but it can be difficult to obtain a homogeneous mixture. It is also known to use a particular type of dispenser with a metered neck. These dispensers are filled with fuel and then topped up with the required amount of oil. The can/bottle is then shaken to ensure a homogeneous mix. Once the oil and fuel have been mixed, it is difficult to change the concentration of oil in the fuel if the wrong amount of oil has been added or a different concentration of oil in the fuel is required.